dtls: Fix memcmp() arguments in MTU detection code
dtls: Fix memcmp() arguments in MTU detection code

Fix the length argument and return value checks.  Caught by clang
warnings.

Signed-off-by: Kevin Cernekee <3105dbb3dd63fbb4f6371cfb04adc6726f76c56b@gmail.com>
Signed-off-by: David Woodhouse <b460d66aaf00c296a3db1c1d9eeafc081d5f7d70@intel.com>

nmav/openconnect-mine,brandt/openconnect,cernekee/openconnect,mtmiller/openconnect,nmav/openconnect-mine,mtmiller/openconnect,mtmiller/openconnect,nmav/openconnect-mine,mtmiller/openconnect,brandt/openconnect,cernekee/openconnect,brandt/openconnect,cernekee/openconnect,nmav/openconnect-mine,cernekee/openconnect,brandt/openconnect